Conventionally, light emitting apparatuses such as LEDs, LDs, etc. are known that employ gallium-nitride (GaN)-based compound semiconductor. As to the emission of light and oscillation having a wavelength in a wavelength region of 380 nm or below, the light emission wavelength of the emission of light and the oscillation is varied by varying the composition ratio of “In” in a GaN-based compound semiconductor including In constituting an active layer and, more specifically, the wavelength is shortened by reducing the composition ratio of In.
FIGS. 9A, 9B, 10A and 10B show the construction of a light-emitting apparatus (semiconductor laser) described in the patent literature listed below. In FIGS. 9A and 9B, FIG. 9A shows a cross-sectional view of the construction of the light-emitting apparatus and FIG. 9B shows the composition ratio of Al in this cross-sectional construction. This light-emitting apparatus has the construction formed by stacking a first-conducting-type layer 11, an active layer 12, and a second-conducting-type layer 13 on a substrate 21 and a buffer layer 22.
The first-conducting-type layer 11 comprises a contact layer 23, a clad layer 25, and a fist light-guiding layer 26. The active layer 12 comprises an active layer 27. The second-conducting-type layer 13 comprises a carrier-confining layer 28, a second light-guiding layer 29, a clad layer 30, and a contact layer 31. The first and second light-guiding layers 26 and 29 sandwich the active layer 12 (or the actively layer 27) in this construction and the first and second light-guiding layers and the active layer therebetween form a light-guiding path.
FIGS. 10A and 10B show the layer structure in the vicinity of the active layer 12 (or the active layer 27) and the band gaps of the layer structure. The active layer 12 (27) has a construction formed by alternately stacking a plurality of well layers 1a and 1b and a plurality of barrier layers 2a, 2b and 2c, and the carrier-confining layer 28 is further formed in the active layer 27 or in the vicinity of the active layer. The carrier-confining layer 28 confines carriers from the first-conducting-type layer in the active layer or the well layers. In a device for which it is assumed that the first-conducting-type layer is n-type and the second-conducting-type layer is p-type, the carrier-confining layer 28 confines electrons into the active layer. Additionally, there is description that the carrier-confining layer 28 is provided on the p-type layer side because electrons tend to overflow the active layer more easily than holes, because the diffusion length of electrons is longer compared to the diffusion length of holes in a nitride semiconductor.
There is also description that, when a carrier-confining layer is provided on the n-type layer side, it is not necessary to provide a large offset between the active layer and the barrier layer like the carrier-confining layer on the p-type layer side, and the barrier layer 2a arranged most closely to the n-type side in the active layer can be caused to functioned as a hole-confining layer, and that the carrier-confining function of the n-type-side barrier layer 2a can be preferably drawn out by increasing the film thickness of the barrier layer 2a compared to the other barrier layers (see, e.g., Japanese Patent Application Laid-Open Publication No. 2003-115642).